1. Field of the Invention
The present invention relates to an air conditioning system with two compressors and a method for operating the same, and more particularly to an air conditioning system with two compressors, so as to shorten standby time for re-operating a stopped compressor, and a method for operating the air conditioning system.
2. Description of the Related Art
Generally, an air conditioner comprises a compressor for compressing a gaseous refrigerant in a low-temperature and low-pressure state so as to convert it into a high-temperature and high-pressure state, a condenser for condensing the gaseous refrigerant in the high-temperature and high-pressure state compressed by the compressor so as to convert it into a liquid refrigerant in a high-temperature and high-pressure state, and an evaporator for evaporating the liquid refrigerant in the high-temperature and high-pressure state condensed by the condenser so as to convert it into a gaseous refrigerant in a low-temperature and low-pressure state. A heat pump air conditioner, additionally having a heating function, further comprises a four-way valve for converting a flow direction of the refrigerant according to cooling and heating modes.
In such a heat pump air conditioner, an indoor heat exchanger and an outdoor heat exchanger have different functions according to their cooling and heating modes. That is, the indoor heat exchanger serves as the condenser and the outdoor heat exchanger serves as the evaporator in the heating mode, thereby forming a heating cycle. On the other hand, the indoor heat exchanger serves as the evaporator and the outdoor heat exchanger serves as the condenser in the cooling mode, thereby forming a cooling cycle. Therefore, the heat pump air conditioner is unlimitedly applicable in all seasons.
Hereinafter, the air conditioner for forming the cooling cycle and the heat pump air conditioner for forming the cooling and heating cycles are generally referred to as an air conditioner.
Recent, air conditioners employ a plurality of compressors having different capacities, thereby variably changing a compression capacity of the refrigerant and optimizing cooling and heating efficiencies.
FIG. 1 is a block diagram illustrating a flow of a refrigerant of a conventional air conditioner in a cooling mode, and FIG. 2 is a graph illustrating operating states of compressors in the conventional air conditioner. With reference to FIGS. 1 and 2, a method for operating the conventional air conditioner is described, as follows.
FIG. 1 is a block diagram illustrating the flow of the refrigerant of the conventional air conditioner in the cooling mode. The conventional air conditioner comprises a plurality of compressors 10 for compressing a gaseous refrigerant in a low-temperature and low-pressure state so as to convert it into a high-temperature and high-pressure state. The compressors 10 includes first and second compressors 11 and 12, having different compression capacities of the refrigerant.
Each of the first and second compressors 11 and 12 has a designated compression capacity of the refrigerant, so as to compress a specific percentage of the total capacity (100%) of the refrigerant. The compression capacities of the refrigerant of the first and second compressors 11 and 12 are set by a manufacturer. Herein, the first compressor 11 has a 60% compression capacity of the refrigerant, and the second compressor 12 has a 40% compression capacity of the refrigerant.
Therefore, the total compression capacity of the refrigerant in the air conditioner is variably changed by selectively or simultaneously operating the first compressor 11 and the second compressor 12 according to a cooling load.
The conventional air conditioner further comprises check valves 13 and 14, a four-way valve 20, an outdoor heat exchanger 30, an expansion valve 40, an indoor heat exchanger 50, and an accumulator 60, thereby forming a cooling cycle via a flow of the refrigerant. The check valves 13 and 14 respectively prevent the reverse-flow of the refrigerant compressed by the first and second compressors 11 and 12. The four-way valve 20 converts the flow direction of the refrigerant passing through the first and second compressors 11 and 12, thereby reversing functions of the outdoor and indoor heat exchangers 30 and 50. The outdoor heat exchanger 30 exchanges heat between external air and the refrigerant, thereby condensing the gaseous refrigerant in the high-temperature and high-pressure state, so as to convert it into a liquid refrigerant in a mid-temperature and high-pressure state. The expansion valve 40 decompresses the liquid refrigerant passing through the outdoor heat exchanger 30, so as to convert it into a low-temperature and low-pressure state. The indoor heat exchanger 50 exchanges heat between the indoor air and the refrigerant passing through the expansion valve 40 so as to convert it into a two-phase refrigerant in liquid and gaseous phases. The accumulator 60 separates the liquid phase from the two-phase refrigerant passing through the indoor heat exchanger 50, and then supplies only the gaseous phase to the first and second compressors 11 and 12.
When the cooling or heating load is relatively light, only the second compressor 12 of the air conditioner is operated. Herein, the first compressor 11 is stopped, and the check valve 13 of the first compressor 11 is closed.
Therefore, the gaseous refrigerant compressed in the high-pressure state, which is discharged from an outlet 11b of the first compressor 11 and then supplied to the check valve 13, is cut off, and then high pressure at the outlet 11b of the first compressor 11 is maintained. Since the gaseous refrigerant at an inlet 11a of the first compressor 11 is not yet compressed, low pressure at an inlet 11a of the first compressor 11 is maintained. Therefore, a pressure difference between the inlet 11a and the outlet 11b of the compressor 11 is generated.
When the pressures at the inlet 11a and the outlet 11b of the compressor 11 are equalized so as to remove the pressure difference, the stopped compressor 11 is re-operated. Standby time for re-operating the stopped compressor 11 is the same as the time taken to equalize the pressures at the inlet 11a and the outlet 11b of the compressor 11.
When the high-pressure refrigerant around the outlet 11b moves toward the inlet 11a during the pressure equilibrium time, so as to equalize the pressures at the inlet 11a and the outlet 11b of the compressor 11, oil used to operate the first compressor 11 leaks via gaps formed through the first compressor 11 and is accumulated in a pipe (P1) connected to the inlet 11a. When the first compressor 11 is re-operated and the refrigerant flows into the first compressor 11 via the inlet 11a, the leaking oil accumulated in the pipe (P1) flows into the first compressor 11, together with the refrigerant.
However, when the first compressor 11 is stopped for a long time, the leaking oil accumulated in the pipe (P1) is solidified and an inner surface of the pipe (P1) becomes uneven. The uneven inner surface of the pipe (P1) with the solidified oil obstructs the flow of the refrigerant to re-operate the first compressor 11, thereby extending the standby time for re-operating the stopped compressor 11. Further, when the standby time is extended, the air conditioner cannot rapidly cope with the variation of the cooling load, thereby not satisfying users"" comfort requirement within a room.
With reference to FIG. 2, the operating states of the compressors of the conventional air conditioner is described as follows.
When a cooling order is inputted to the air conditioner and the compressors are operated, the second compressor having the 40% compression capacity of the refrigerant is first operated, and later the first compressor having the 60% compression capacity of the refrigerant is additionally operated. Then, the total compression capacity of the refrigerant becomes 100% (F1) and a cooling cycle starts so that the room temperature reaches a desired temperature.
When the room temperature reaches the desired temperature, the compressors are stopped. Then, when the room temperature rises, the compressors are simultaneously operated again so as to lower the room temperature, and later only one compressor is continuously operated so as to maintain the lowered room temperature. Herein, the second compressor is continuously operated and the first compressor is stopped for a long time (PT).
In order to satisfy an increased cooling load, the stopped first compressor must be additionally re-operated together with the second compressor. At this time, standby time for re-operating the stopped first compressor is extended due to the above-described problem, and then the increased cooling load is not rapidly satisfied.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an air conditioning system with two compressors and a method for operating the same, in which standby time for re-operating a stopped compressor is shortened by forcibly operating the stopped compressor regardless of cooling load when the stopped compressor maintains its stopped state for longer than a designated time, thereby rapidly satisfying the variation of the cooling load and improving users"" comfort in a room.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an air conditioning system with two compressors, comprising:
an air conditioner for conditioning air of a room so as to satisfy cooling load via a cooling cycle formed by a refrigerant passing through compressors, a condenser, an expansion valve, and an evaporator; and
a control unit for selectively or simultaneously operating the compressors according to a variation of the cooling load so as to variably control a compression capacity of the refrigerant.
In accordance with another aspect of the present invention, there is provided a method for operating an air conditioning system with two compressors, comprising:
the first step of simultaneously operating the compressors regardless of cooling load at an early stage of the operation;
the second step of selectively operating one of the compressors according to the cooling load; and
the third step of additionally re-operating the stopped compressor when the operated compressor selected from the compressor in the second step is continuously operated for longer than a designated time.